Circuit breakers are one of a variety of overcurrent protection devices used for circuit protection and isolation. The circuit breaker provides electrical protection whenever an electric abnormality occurs. In a circuit breaker, current enters the system from a power line and passes through a line conductor to a stationary contact fixed on the line conductor, then to a movable contact. The movable contact can be fixedly attached to an arm and the arm can be mounted to a rotor. As long as the stationary and movable contacts are in physical contact, current passes from the stationary contact to the movable contact and out of the circuit breaker to down line electrical devices.
In the event of an overcurrent condition (e.g., a short circuit), extremely high electromagnetic forces can be generated. The electromagnetic forces repel the movable contact away from the stationary contact. Because the movable contact is fixedly attached to a rotating arm, the arm pivots and physically separates the stationary and movable contacts thus tripping the circuit. Upon separation of the contacts and blowing open the circuit, an arcing condition occurs. The breaker's trip unit will trip the breaker which will cause the contacts to separate. Also, arcing occurs during normal “ON/OFF” operations on the breaker. It is desirable to suppress resultant arcs.
A typical method of suppressing the arc is to direct it into an arc chute, which is generally a series of metal plates that dissipate the energy of the arc. This arc chute is situated proximate to the stationary contact point of the circuit. An arc runner is used to direct the arc to the arc chute. The arc runner covers the exposed area of the line conductor. Since the arc runner provides a pathway for the arc to follow to the arc chute, it is subject to intensely high temperatures.
During higher fault interruptions, particularly those associated with DC currents, the arc can be resistant to movement into the arc chute because the magnetic field created by the permanent magnets in the arc chute may not be sufficiently strong against the gas dynamic force to push and stretch the arc into lower arc plates. The lack of engagement between the arc and the lower arc plates may cause longer arcing time and damage to the arc chute and breaker.